1. Field of the Invention
The present invention relates to an ion implanter and, more particularly, to an ion implanter provided with a to-and-fro wafer disk for supporting a wafer to be subjected to ion implantation.
2. Description of the Related Art
In a conventional ion implanter, a plurality of wafers are mounted in a circumferential arrangement on a rotary disk, the rotary disk is rotated and moved alternately in opposite directions to implant ions uniformly in all the wafers. A metronome type swinging mechanism for swinging the rotary disk alternately in opposite directions disclosed in JP-A No. Hei 8-329879 drives a reversible shaft disposed on a level below the center of gravity of the rotary disk by a motor or the like to swing the rotary disk alternately in opposite directions in a vertical plane. This metronome type swinging mechanism varies the moving speed of the rotary disk according to the position of the wafer subjected to ion implantation in order that ions are implanted uniformly in all the wafers.
An ion implanter, particularly, a SiMOX ion implanter that implants oxygen ions in silicon wafers is required to be capable of implanting oxygen ions in wafers in a highly accurate uniformity at a high throughput. When reversing the rotary disk in a to-and-fro motion, the direction and magnitude of the speed of the rotary disk change suddenly, and consequently, the speed of the rotary disk varies. Therefore, ion implantation is interrupted in a reversing range in which the moving direction of the rotary disk is reversed, whereby the ions can be implanted in the wafers supported on the rotary disk in a highly accurate uniformity only in a moving range in which the rotary disk moves at a predetermined speed. However, the interruption of ion implantation while the rotary disk is moving in the reversing range causes a time loss and reduces throughput.
Accordingly, it is an object of the present invention to provide an ion implanter capable of implanting ions in wafers in a highly accurate uniformity and to carry out an ion implantation process at a high throughput.
With the foregoing object in view, the present invention provides an ion implanter including an ion source, and a wafer support device having a rotary disk that supports a plurality of wafers thereon and is rotated about its center axis, and capable of being swung alternately in opposite directions, wherein an ion beam emitted by the ion source is projected on the wafers for ion implantation, the wafer support device is supported so that a component of the gravitational acceleration imparted to the wafer support device acts in the same direction as that of a force applied to the wafer support device to reverse the same.
Since the gravitational acceleration is imparted at all times to the wafer support device, the gravitational acceleration assists the force applied to the wafer support device when reversing the wafer support. Consequently, load that acts on the wafer support device when the wafer support device is reversed is reduced, time loss is reduced and the throughput of the ion implanter is improved.
According to the present invention, it is preferable that the center of gravity of the wafer support device should lie below an axis about which the wafer support device is swung alternately in opposite directions.
When the wafer support device is thus disposed, the component of the gravitational acceleration imparted to the wafer support device acts in the same direction as that of the force that is applied to the wafer support device to reverse the same.